Good news! A new Sacred Music Retreat was brought to my attention that you might find interesting. It is at the Oratory in Cincinnati, from August 8th to 12th, the cost is $450 (includes room and meals). The focus will be on singing for the Extraordinary Form Mass, as well as the Divine Office. This is a wonderful opportunity to obtain experience not only with chant, but also with motets and polyphony. Registration ends on June 30th, though late registration ($495) is available till July 16th (there are a limited number of spots, so be sure to sign up sooner rather than later). Check out the link below for complete details.
https://www.oldstmarys.org/2018/05/16/2405/
St. Augustine's Schola 